"초(s)" refers to the unit of time known as a second, which is a fundamental measurement in the International System of Units (SI). It is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom. Seconds are commonly used to measure time in everyday life, from clocks to timers. In addition to being a basic unit of time, seconds are often used in various fields such as science, sports, and music. For example, in athletics, race times are recorded in seconds, while in music, tempo is often indicated in beats per minute, which can be converted to seconds for precise timing.